GPS TEC measurements over Purulia, West Bengal,India

1. Initial results of GNSS-based Total Electron Content (TEC) monitoring from Purulia, West
Bengal
Supratick Adhikary1,2,Sushanta Kumar Mondal 1 ,Sujay Pal2,3
ABSTRACT
Initial results of monitoring of
ionospheric Total Electron
Content (TEC) from Purulia,
West Bengal (23.3322° N,
86.3616° E) located within the
northern crest of equatorial
ionization anomaly (EIA) region
are presented here. A multi-
frequency and multi-
constellation high-end NovAtel
GNSS receiver has been
installed at the Department of
Physics, SKBU, Purulia in late
2017 for space weather
monitoring. The measurement
of GNSS-based TEC is
important not only to correct
range-delay errors introduced
by the ionosphere but also to
monitor the state of the
ionosphere continuously. A
preliminary analysis of GPS
TEC data of 2018 and 2019
has been done here. Mainly,
the diurnal and seasonal
variations of vertical TEC at
Purulia are presented and then
compared with the IRI-2016
model. Further, TEC variation
obtained from the GALILEO
and GLONASS constellations
are also compared.
CONTACT
Dr. Sushanta K. Mondal
Sidho-Kanho-Birsha
university, Purulia
1 Sidho-Kanho-Birsha University, Purulia, WB 2Department of Physics, Srikrishna College, Bagula, Nadia, WB; 3Near-Earth Space and Atmospheric Observatory
(NESAO),WB
PS2: NSSS-20211219041200
DATA & METHOD RESULTS
 A multi-frequency high end NovAtel GNSS receiver
has been installed at Purulia (Lat:23.33N, 86.36E)
in October 2017.
 The 120-channel multi-constellation, multi-frequency OEM628
receiver measures ionospheric scintillations and TEC for the
following tracked signal types GPS L1-C/A, L2-P(Y), L2C, L5Q;
GLONASS L1, L2; Galileo E1, E5a, E5b, ALTBOC, E6; SBAS L1, L2.
 The receiver records raw data of 50 Hz phase and amplitude and
1 Hz TEC measurements every one second.
 Every 60 seconds the receiver outputs detail summary messages
and further information and calculation for individual tracked
signals, including SV azimuth/elevation angle, C/N0, lock time,
code-minus-carrier, calculations of different amplitude
scintillation (S4 ), phase scintillation and TEC statistics.
 GNSS data recorded during 2018-2019 have been used for
preliminary analysis.
 Diurnal variation of TEC
 GNSS receiver gives the slant TEC data at a sampling
rate of 60 s. The vertical TEC (VTEC) values are
obtained at different ionospheric pierce point (IPP)
locations by using the very well-known mapping function:
where hs is the effective ionospheric height taken as 350
km here.
 Daily variation of VTEC have been
obtained for all available data of the GPS
and GLONASS constellations.
 As an example, we have plotted the diurnal
variations of all available dates from May 2019.
 Comparison with the IRI-2016 Model
RESULTS
 The diurnal maximum occurred around
~8.5UT (14 LT) and the minimum occurred
around 20-22 UT (1.5 - 3.5 LT). The monthly
mean diurnal polt is indicated by the red curve.
 Monthly variation of TEC
Fig.1
Fig.2
Fig.4
 Seasonal variation of TEC
Fig.3
 Fig.3 shows the diurnal
variations of monthly
mean VTEC obtained
for every month of
2019. The highest
value of VTEC has
been observed on
March and April.onth.
The ionosphere exhibits
strong seasonal variations
on account of solar zenith
angle or the solar radiations
flux change. It is clearly seen
from Fig.4 that that VTEC
has highest value in equinox
period which is obtained
by averaging the monthly mean
diurnal curves of March and September.
The VTEC during the Spring period obtained by averaging March,
April and May, has also the same value as of equinox excpet for
mid-day. The VTEC value is the lowest in summer months (June,
July, August). The highest electron density observed in equinox is
due to the winter anomaly in seasonal variation. The time of
occurrence of the diurnal maximum also varies with season.
We have compared the seasonal
variation of GPS VTEC at Purulia with
the VTEC values obtained from the
International Reference Ionosphere
(IRI-2016) model. We have set the
upper boundary of the ionosphere in
the IRI-model as 400 km.
IRI-2016 model underestimates the
values of GPS-TEC in Spring, Summer
and Winter. Though the IRI model
estimates almost same peak value of
VTEC during Spring.
The highest value of GPS TEC has been found
in spring and lowest in summer whereas the
highest value of TEC obtained from IRI- model
has also been
found in spring and lowest in summer.
Acknowledgement: Authors thank www.irimodel.org for the IRI-2016 code.
S. K. Mondal acknowledges the financial support from the SKB University.
Authors also thank Prof. Ashik Paul of University of Calcutta for having
valuable discussions with GNSS studies.